through games of 1/8/07

Beginning with Football Outsiders Almanac 2009, Brian Fremeau and Bill Connelly, originators of Football Outsiders' two statistical approaches -- FEI and S&P+, respectively -- began to create a combined ranking that would serve as Football Outsiders' 'official' college football rankings.

The Fremeau Efficiency Index (FEI) considers each of the nearly 20,000 possessions every season in major college football. All drives are filtered to eliminate first-half clock-kills and end-of-game garbage drives and scores. A scoring rate analysis of the remaining possessions then determines the baseline possession efficiency expectations against which each team is measured. A team is rewarded for playing well against good teams, win or lose, and is punished more severely for playing poorly against bad teams than it is rewarded for playing well against bad teams.

The S&P+ Ratings are a college football ratings system derived from both play-by-play and drive data from all 800+ of a season's FBS college football games (and 140,000+ plays). There are four key components to the S&P+:

Success Rate: A common Football Outsiders tool used to measure efficiency by determining whether every play of a given game was successful or not. The terms of success in college football: 50 percent of necessary yardage on first down, 70 percent on second down, and 100 percent on third and fourth down.

EqPts Per Play (PPP): An explosiveness measure derived from determining the point value of every yard line (based on the expected number of points an offense could expect to score from that yard line) and, therefore, every play of a given game.

Drive Efficiency: As of February 2013, S&P+ also includes a drive-based aspect based on the field position a team creates and its average success at scoring or preventing the points expected based on that field position.

Opponent adjustments: Success Rate and PPP combine to form S&P, an OPS-like measure for football. Then each team's S&P output for a given category (Rushing/Passing on either Standard Downs or Passing Downs) is compared to the expected output based upon their opponents and their opponents' opponents. This is a schedule-based adjustment designed to reward tougher schedules and punish weaker ones.

Special Teams F/+ has been added to the overall F/+ formula starting with 2007. It is a direct offshoot of the Special Teams Efficiency rating found on the FEI page. To read about the rationale behind this adjustment, go here. For years before 2007, an even combination of S&P+ and FEI is used.